title: Studies of kinetics and equilibrium membrane binding of class A and class L model amphipathic peptides.
abstract: We studied the kinetics and equilibrium membrane binding of two amphipathic alpha-helical peptides: the 18L peptide, which belongs to the class L (lytic peptides), and the Ac-18A-NH2 peptide of the class A (apolipoprotein), according to classification of Segrest et al. ((1990) Proteins, 8, 103-117). Both for cationic 18L and zwitterionic Ac-18A-NH2, the presence of acidic lipids increased the membrane binding constants by two orders of magnitude. The free energy of peptide-membrane association was in the range of 8.5-12.8 kcal/mol. Binding isotherms corresponded to monomer partitioning with saturation at high peptide/lipid ratios. This was also supported by stopped flow studies of the kinetics of peptide-membrane association as measured by peptide tryptophan fluorescence or by energy transfer from the peptide to the lipid-anchored anthrylvinyl fluorophor. The apparent time required for peptide-membrane equilibration was in the millisecond range. At low peptide/lipid ratios it depended on lipid concentration and was independent of the peptide concentration. The rate of peptide-membrane association was found to be relatively close to the diffusion limit. Thus peptide-membrane affinity was mostly determined by the peptide dissociation rate, i.e. higher membrane affinity correlated with a decrease in dissociation rate and with a slower peptide exchange. We have shown that the dynamic character of the peptide membrane equilibrium can be used for selective peptide targeting and disruption of membranes with a specific lipid composition.
authors.affiliation: Department of Biochemistry, McMaster University Health Sciences Center, Hamilton, Ontario, Canada.
authors.forename: I V
authors.initials: IV
authors.lastname: Polozov
authors.forename: A I
authors.initials: AI
authors.lastname: Polozova
authors.forename: V K
authors.initials: VK
authors.lastname: Mishra
authors.forename: G M
authors.initials: GM
authors.lastname: Anantharamaiah
authors.forename: J P
authors.initials: JP
authors.lastname: Segrest
authors.forename: R M
authors.initials: RM
authors.lastname: Epand
mesh_terms: D000595:Amino Acid Sequence; D002412:Cations; D002462:Cell Membrane; D007700:Kinetics; D008081:Liposomes; D008563:Membrane Lipids / Q000737:chemistry*; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D014364:Tryptophan / Q000032:analysis
chemical_list: D002412:Cations; D008081:Liposomes; D008563:Membrane Lipids; D010455:Peptides; C080383:peptide 18A; D014364:Tryptophan